This invention relates to a steel for foundry roll shells, especially for aluminum casting machines.
It has become increasingly common to use scrap for the production of semi-finished aluminum products. For this purpose the scrap is melted, cast and hot rolled. The casting of the aluminum melt is performed in such way that it is poured into the gap between two cooled foundry rolls which are pivoted on horizontal axis. Upon contact with the cooled foundry rolls the aluminium melt solidifies and is shaped by the rotating foundry rolls.
Foundry rolls generally consist of an axis and a foundry roll shell shrinked or mounted thereon. The material used for foundry roll shells must meet certain requirements. One requirement is a low thermal expansion coefficient to ensure an exact positioning of the shell on the axis even at elevated temperatures. Furthermore, the material used for foundry roll shells must be of high hardness and, in addition, show good ductility at elevated temperatures up to 750.degree. C. After prolonged time of operation a network of cracks is formed due to thermal strain. The aim is to prolong the time until unavoidable formation of cracks happens by using a shell of optimum quality. It is thus essential for materials used for foundry roll shells to have a high resistance against hot cracks.
Up to now steels having chemical compositions as described in table 1 have been used for foundry roll shells. All percentages are % by weight.
______________________________________ Alloying elements in %-by weight Steel C Mn Cr Ni Mo V ______________________________________ P911 0.53 0.47 2.05 0.50 1.03 0.35 P912 0.53 0.50 1.13 0.48 0.48 0.15 P914 0.16 0.96 1.40 0.20 0.90 0.26 P916 0.32 0.30 2.95 0.20 2.80 0.20 P917 0.30 0.55 2.55 0.50 1.10 0.60 P918 0.18 0.50 5.00 0.15 1.10 0.90 ______________________________________
The steels listed in table 1 are chromium-, nickel-, molybdenum- and vanadium-alloyed steels having a carbon content of 0.16% and higher. By use of these steels it was possible to adjust the desired properties of the foundry roll shells in a satisfactory manner.
It is one object of the present invention to further improve the steels presently known in the art for use in foundry roll shells so that the foundry roll shells exhibit an improved resistance against mechanical wear and against hot cracks and thereby have an extended life time.